QuestionIt is well known that if one does not use a bicycle or car the tires go flat. On the other hand, if, for a much longer time, the vehicle is used; then the tires do not go flat.
I believe this occurs with both tubed and tubeless bike tires. Don't know of any car tubed tires.
Why does this flattening occur? On the other hand; why does flattening not occur when the tires are used?
Gene Leboy
6400 Taylor Rd Unit 245
Punta Gorda, FL 33950
(941) 637 8915
elleboy@sunline.net
AnswerGene,
First, I'm going to reject your premise that tires that are unused go flat faster - That has not been my experience. I think what may lead to that conclusion is that vehicles that are idle are 1) not maintained at all, 2) the tires are probably old on these vehicles and old tires will develop cracks making them leak faster and 3) you won't recall that someone may have done a little maintenance including filling up the tires, where you will remember the flat on a vehicle sitting idle.
The basic mechanism is that rubber is not 100% air tight. And different rubbers have different air permeabilities - which is why there is a special type of rubber (butyl) on the inside of a tire to improve the air retention. Butyl is the same stuff used in tubes.
So tires will leak very slowly. But as tires age they will develop cracks, which increases the surface area, which speeds up the leakage. So if a crack developes on the inside, the barrier has been breached and the leakage accelerates.
And there is a point where the deflection of the tire is such that the bead will distort and air will leak out between the tire and the rim.
Hopefully this answers your question.
